We are utilizing an in vitro system of normal and transformed human cells for testing various chemotherapeutic strategems and for studying certain aspects of differential growth control. In our system one combination of drugs will selectively kill transformed human cells while allowing normal cells to survive. We plan to pursue the basis of selective toxicity in vitro and hope to suggest rationales for combination chemotherapy based on our findings. A second area of interest is the biological manifestations of DNA damage as measured by mutation analysis. We have found that BCNU and MNU are mutagenic in V79 CHL cells. Mutagenicity and DNA strand-breakage seem to be correlated in this system.